Rough, Unstable, Or Incorrect Idle, Stalling Symptom - Mercury MerCruiser MCM 454 Mag MPI Service Manual

SERVICE MANUAL NUMBER 23
Cuts Out, Misses Symptom (Continued)

Rough, Unstable, or Incorrect Idle, Stalling Symptom

Step
Definition: Engine runs unevenly at idle. If severe, the engine or vessel may shake.
Engine idle speed may vary in rpm. Either condition may be severe enough to stall the
engine.
Index
90-861326--1 MARCH 1999
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1. Check for Electromagnetic Interfer-
ence (EMI). A missing condition can
be caused by EMI on the reference
circuit. EMI can usually be detected
by monitoring engine rpm with a
scan tool or tachometer. A sudden
11
increase in rpm with little change in
actual engine rpm change, indicates
EMI is present.
2. If EMI is present, locate and repair
the source.
Was a problem found?
1. Review all diagnostic procedures
within this table.
2. If all procedures have been com-
pleted and no malfunctions have
been found, review/inspect the fol-
lowing:
Visual/physical inspection.
12
Scan tool data.
All electrical connections within a
suspected circuit and/or system.
3. If a problem is found, repair as nec-
essary.
Was a problem found?
Action
Was the "On-Board Diagnostic" (OBD)
1
System Check performed?
Was visual/physical check performed?
2
1. Check for proper operation of the
IAC valve.
Refer to Table A-8 in "General Sys-
3 tem Diagnostics" section.
2. If a problem is found, repair as nec-
essary.
Was a problem found?
1. Check for proper operation of Igni-
tion Control (IC) circuit and the
Knock Sensor (KS) circuit.
4
2. If a problem is found, repair as nec-
essary.
Was a problem found?
FUEL INJECTION SYSTEM TROUBLESHOOTING
Go to OBD
System
-
Check
Go to OBD
System
-
Check
Value(s) Yes
- Go to Step 2
- Go to Step 3
Go to OBD
System
-
Check
Go to OBD
System
-
Check
Go to Step 12
Contact
MerCruiser
Customer
Service
No
Go to OBD
System Check
Go to Visual/
Physical
Check
Go to Step 4
Go to Step 5
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